HEI been mentioned a couple times - Bought mine thru this seller: http://www.ebay.com/sch/bestvalueho...h=item20cb1d0c0c&rt=nc&_trksid=p2047675.l2562
Something I haven't seen mentioned so far and can really effect the power on a 235 is point gap and timing. My 235 had the same issues as yours - just did a basic tune-up and it made a huge difference. Start with your point gap (I assume you're still running a stock-type distributor). Points should be set at .018, just turn the engine by hand until the points are sitting on one of the 6 lobes (wide open) and adjust the gap by loosening the breaker plate hold down screw. Then set the base-line timing by aiming the timing light at the hole in the bell housing (just above the starter) and turning the distributor base (after you loosen the hold-down bolt) until the "BB" lines up with the pointer. At this point you have it set by the book, but any Chevy guy will tell you that they run a whole lot better with more advance. Bump the timing ahead a little (by moving the distributor a little CCW) and take it for a drive. What you want is to be able to accellerate hard in high gear without any pinging. They'll take a lot more advance than the base line setting and will run better and get better mileage too. This may take a few trial and error runs but you'll eventually find your engines sweet spot. I put a timing light on my 235 after this procedure and I can't even see the "BB" anymore but it runs like a champ. Sorry for the long post, good luck!!
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